This invention relates generally to security systems, and more particularly, to door proximity sensors used in security systems.
Security systems are typically used to monitor and control entry and exit points within a building, as well as perform other functions such as fire and smoke detection. A sensor is typically installed proximate to each door that is to be monitored. Several types of sensors may be used to detect whether the door is open or closed by detecting the proximity of the door.
For example, a mechanical contact, a reed switch/magnet combination, or an infrared (IR) sensor may be installed. Unfortunately, each of these sensors may be defeated by a person having limited knowledge of the sensor and/or security system. Mechanical contacts can be easily defeated by using a strip of metal or other material to depress the contact and keep it actuated while the door is compromised. Also, reed switch/magnet combinations may be defeated from the outside by using an additional magnet to keep the reed switch actuated. IR sensors have been used which constantly transmit IR, then compare the received or reflected IR to the transmitted IR. The IR sensors may be defeated by shining a light, such as a flashlight, at the IR sensor. Sunlight may also cause interference.
Therefore, a need exists for a door and/or proximity sensor which eliminates intentional or inadvertent interference. Certain embodiments of the present invention are intended to meet these needs and other objectives that will become apparent from the description and drawings set forth below.